Hi guys, I've completed the install and it was not exactly a piece of cake. Fortunately, I was able to find just enough info here and at Swedespeed to get it done. I wanted to keep the factory head unit and just install a subwoofer. I chose the Rockville RVE12CA because it was an all-in-one 12 inch subwoofer with built-in 350w amp, ported and affordable. This thing "properly installed" has drastically improved the sound and looks great. Not exactly factory looking but worked well given the limited trunk space available.
I bolted a pair of hinges to the sub to keep it in place and to give myself options for listening and storage needs.
I initially used the high ouput connection that came with the Rockville but experienced an issue where the sub would "heartbeat" sound only with no audio. Unplugging and replugging the high output speaker connector would fix it, but sub did not sound very good. I tried a new ground and new speaker wire but it did not fix the issue. Finally, after some research I landed on this Line Output Converter:
Switching from high output to low output RCA ouputs fixed my issue and sounded much better. Highly recommend this config to anyone who has a High Performance factory audio system and wants more bass for under $200 US. Thanks again to those who posted helpful threads and offered guidance.